Recently various kinds of radio telephone have been developed. One of these is generally referred to as a mobile telephone. The mobile radio telephone, which may be mounted in a car, a train, a ship or the like, comprises a transceiver unit with an antenna and telephone unit including a handset and a base unit. These units are physically separated and are connected by signal lines to one other.
Another kind of radio telephone is referred to as a portable telephone. Portable telephones may be further divided into two groups: a transportable type and a handheld type. In the transportable type of portable radio telephone, a transceiver unit is combined into a main unit of a telephone unit and an antenna is attached to the main unit; consequently a user may carry the transportable telephone wherever the user goes. In the handheld type of portable radio telephone, all components are compacted into one unit which may be held in the hand of a user. All of these radio telephones are supplied power from a battery. Differentiated from the kinds of radio telephone mentioned above, there is yet a further kind of radio telephone, namely a cordless telephone. The cordless telephone has one or more base units connected to one or more land lines and one or more handheld units. The handheld unit communicates with another telephone apparatus by first establishing a radio channel with the base unit. The handheld unit of a cordless telephone is also supplied power with a battery.
Generally, it is required to reduce consumption of electric power in a radio telephone since a battery installed therein or in a vehicle has a limited power capacity.
In the case of a mobile telephone in a car, a battery mounted in the car is rechargeable as long as the car runs. However when the car ignition is turned off and the car is parked the user may leave the mobile telephone turned on by entering a certain command on the key pad. In such a situation, the mobile telephone consumes the power of the battery wastefully. The power consumption may drain the battery to the extent that the car will not start.
Another problem unsolved by prior art mobile telephone apparatus is introduced when the automobile is removed from the serving area of the mobile telephone service provider. In such a situation, the apparatus may continue to drain battery energy even though the mobile telephone apparatus may be useless.
In the case of either a portable telephone or a hand-held unit of cordless telephone, the consumption of battery power is a more serious problem because these have only a limited power capacity.